Why does pregnancy lead to water retention and constipation? It's not fair to the mother, but does it serve a biological purpose? In strikingly bold colors researchers at the University of Cambridge have found the answers to these questions.
Humans have about 500 million neurons that control our intestinal behavior, an overwhelmingly large number that complicates the research into bloating and constipation. Fruit flies are much simpler and yet like humans, pregnant fruit flies are plagued by constipation and water retention. Dr. Irene Miguel Aliaga and her colleagues at Cambridge University have studied fruit flies as models for humans. They have created a slew of genetically modified fruit flies with intestinal neurons that light up when they are used, and that can be switched on -and off- by the researchers. Photographs of the stained fruit fly guts with fluorescent neurons, such as the ones shown here, were used to locate the neurons that were responsible for regulating appetite and adjusting intestinal water balance during pregnancy.

The female fruit flies have no way of expressing their discomfort and so Dr. Aliaga and her students have to collect all the fly feces and determine their constituency, water content and protein content. A rather unpleasant job you might think, but no says the good doctor, "the flies fecal deposits are actually rather pretty and don't smell bad".

According to the fluorescent intestinal neurons and fruit fly poop analysis it's the fruit fly dad who is responsible for that bloated feeling experienced by the pregnant mom. During copulation he passes along his sperm as well as some hormones. One of the hormones switches on a set of intestinal neurons that are responsible slowing down the gut emptying rate, resulting in constipation, and so even though pregnant fruit flies are eating more food during pregnancy the contents of their intestines become more concentrated. This allows the pregnant mother to absorb the maximum amount of nutrition. The same hormones also result in water retention and bloating.

Similar behavior is observed in humans. And the color-coding of the neurons in fruit flies actually helps us understand it. So if you are pregnant, bloated and constipated, it might be good to know that the food you crave isn't responsible for your discomfort, it's a healthy dose of evolution and sex hormones ensuring that the fetus maximizes its nutritional absorption.